Democratic-aligned groups outspent Republican-aligned groups by 4-to-1 in Massachusetts Senate race last year, according to Politico. Both the Democratic and Republican senatorial campaign committees have remained mum on whether they'll obey the pact, according to Politico. The candidates also asked Boston stations to refuse third party advertising for the candidates and WBUR reports that none have agreed to comply.

A Boston Globe editorial declared that "voluntary pacts between dueling candidates rarely work." It pointed out that super PACs can simply ignore the pact and called on Warren and Brown to take responsibility for super PAC ads aired in their name.

In a scathing review of the pact, James Taranto of The Wall Street Journal refers to it as "a conspiracy of silence" and "a suicide pact." Although it's an agreement between two private parties and is therefore constitutional, Taranto concludes that the pact is wrong because it's suppressing political speech.

An editorial in The New York Sun questioned how Republican Karl Rove is going to support Brown now that the pact is in place. It suggested Rove run ads on behalf of Warren to force Warren's campaign to pay half of the costs. The Rove-affiliated group American Crossroads opposed the pact on the basis that it provided loopholes to benefit Warren's backing from unions.

The door opened for third parties to advertise for candidates with the Supreme Court case Citizens United, which allows corporations to donate an unlimited amount of money to super PACs. The group Common Cause is working to have the decision overturned.

Common Cause spokeswoman Mary Boyle told WBUR that the Brown-Warren pact is unlikely to work because third parties are out of the control of Brown and Warren.